Researchers recently identified stark differences in levels of specific gut bacteria in people with dementia. A new study links changes in gut bacteria to dementia.
Our bodies swarm with microscopic visitors. On our skin, in our mouths, deep in our lungs, and, of course, nestled in our digestive systems. The bacteria in the gut have long been known to assist the digestive process, but in recent years, it has become clear that they are involved in much, much more.
With bacteria now implicated in conditions as diverse as diabetes and schizophrenia, we truly are in the age of the microbiome. Recently, researchers in Japan investigated whether gut bacteria might, one day, help in the diagnosis and even treatment of dementia.
Dr. Naoki Saji, from the Center for Comprehensive Care and Research on Memory Disorders at the National Center for Geriatrics and Gerontology in Obu, Japan, led a team of scientists who found lower levels of the genus Bacteroides, which are considered “good” bacteria in patients with dimentia. Bacteroides break down toxic plant material into sugars that the human body can use. Individuals with dementia were also shown to have higher levels of the genus Ruminococcus than those without dementia.
“Although this is an observational study and we assessed a small number of patients, the odds ratio is certainly high, suggesting that gut bacteria may be a target for the prevention of dementia.” This study is not the first to link changes in gut bacteria to dementia, but scientists are still debating exactly how gut bacteria influence the brain.
According to a recent study, consuming garlic helps counteract age-related changes in gut bacteria associated with memory problems. The benefit comes from allyl sulfide, a compound in garlic known for its health benefits.
The gut contains trillions of microorganisms collectively referred to as gut microbiota. Although many studies have shown the importance of these microorganisms in maintaining human health, less is known about health effects linked to gut microbiota changes that come with age.
“Our findings suggest that dietary administration of garlic containing allyl sulfide could help maintain healthy gut microorganisms and improve cognitive health in the elderly,” said Jyotirmaya Behera, PhD, who lead the research team with Neetu Tyagi, PhD, both from University of Louisville.
“The diversity of the gut microbiota is diminished in elderly people, a life stage when neurodegenerative diseases such as Alzheimer’s and Parkinson’s develop and memory and cognitive abilities can decline,” said Tyagi. “We want to better understand how changes in the gut microbiota relate to aging-associated cognitive decline.”
For the study, the researchers gave oral allyl sulfide to mice that were 24 months old, which correlates to people between 56 and 69 years of age. They compared these mice with 4- and 24-month-old mice not receiving the dietary allyl sulfide supplement. The researchers observed that the older mice receiving the garlic compound showed better long- and short-term memory and healthier gut bacteria than the older mice that didn’t receive the treatment. Spatial memory was also impaired in the 24-month-old mice not receiving allyl sulfide.
The researchers found that mice receiving the garlic compound exhibited higher levels of neuronal-derived natriuretic factor (NDNF) gene expression. In addition, recombinant-NDNF protein therapy in the brain restored the cognitive abilities of the older mice that did not receive the garlic compound. The researchers also found that oral allyl sulfide administration produces hydrogen sulfide gas — a messenger molecule that prevents intestinal inflammation — in the gut.
Overall, the new findings suggest that dietary allyl sulfide promotes memory consolidation by restoring gut bacteria. The researchers are continuing to conduct experiments aimed at better understanding the relationship between the gut microbiota and cognitive decline and are examining how garlic might be used as a treatment in the aging human population.
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